The present invention relates generally to radio antennas, and more particularly to an antenna for portable communication devices.
Modern styling trends dictate contradictory requirements in the design of hand-held communication devices such as cellular phones. On the one hand, consumers are very interested in smaller phones with concealed (internal) antennas that are not susceptible to damage by catching on clothing or other objects. On the other hand, it is necessary to achieve adequate antenna electrical performance. In addition, wireless handheld communication devices, such as cellular telephones, transmit RF power and are carefully scrutinized for their level of RF radiation emissions.
Typically, internal antennas are placed on top-rear side of a cellular phone. However, there are two technical problems related to this solution, as phones become increasingly smaller: a) a user""s hand, which holds the phone, almost entirely blocks the antenna. This can deteriorate antenna performance well below acceptable level, and b) internal antennas can excite RF currents on a chassis of the phone, which is placed close to the user. This can require reducing output RF power in order to meet RF exposure standards. Hence, placement of a concealed antenna on top-rear side of a small phone is not recommended.
The highest level of RF exposure is most often from RF currents flowing on or in the conductive parts of the housing of the device and not on the antenna. Prior art methods of reducing or eliminating the RF currents of the housing have resulted in the use of large and unwieldy antennas or large RF currents that cause large reactive near fields of the antenna such that it then becomes the dominant source of RF exposure. In either case, the size of the antenna and phone increases, which is undesirable.
The size of portable communication devices has historically been set by the size of the enclosed electronics and the battery. Consumer and user demand has continued to push a dramatic reduction in the size of communication devices. As a result, during transmission, the antenna induces higher RF current densities onto the small housing, chassis or printed circuit boards of the communication device in an uncontrolled manner. These RF currents are often dissipated rather than efficiently contributing to the radiation of RF communication signals. The dissipation of RF power can detrimentally affect the circuitry on very small units. Moreover, this loss of power lowers the quality of communication and reduces battery life of the device. These problems are compounded when a device and antenna system is required to operate over multiple frequency bands.
Accordingly, what is needed is a communication device having a multi-band antenna configuration that is less likely to experience signal degradation due to use by consumer. In particular, it would be of benefit to provide an antenna that is directed away from the proximity of the user. It would also be beneficial to exclude a phone""s chassis from being a counterpoise for antenna and, hence, reduce RF currents on the phone""s chassis. Additionally, it would be an advantage to accomplish these needs without: reduced antenna efficiency at the talking position, decreased battery life, or increased size or cost of the communication device.